38 



BITTER PIT INVESTIGATION. 



The reason for this extensive distribution of vessels is evident, since the developing fruit 

 must be richly supplied with food-materials, to maintain the rapid growth. The water, containing 

 mineral matter in solution, the so-called "crude sap," is conveyed by the wood-portion of each 

 bundle, with its vessels and tracheids (Fig. 98). The solution of organic food-material, the 

 so-called " elaborated sap," passes along the bast-portion, with its sieve-tubes and associated 

 cells ; and, by means of numerous cross connexions between the two kinds of tissues, there is a 

 blending of the " crude " and " elaborated " saps, which results in the formation of proteid 

 substance ; and this, in contact with the living protoplasm, becomes converted into the living 

 substance itself. 



The vascular system must not be conceived of as a vast network of tubes conveying 

 food-material to a definite terminus, but as being tapped on the way by living tissues wherever 

 growth is going on, or storage is required. The movement of the food-materials takes place in 

 whatever direction supplies are wanted, and even in the same cell or vessel there may be a flow 

 in opposite directions at the same time. 



VASCULAR BUNDLES IN RELATION TO THE SEEDS. 



That the vascular bundles are developed primarily in connexion with the " core " 

 comprising the carpels, and gradually spread out into the fleshy receptacle, is evident from various 

 considerations. When a coloured fluid is injected into the stalk of the apple, it first spreads out 

 into the cavity containing the seeds, and thus the " pips " or seeds are the first to be supplied with 

 the nutritive fluid. But very striking evidence is also afforded that the development of the seed 

 influences the growth of the fleshy receptacle, for when only some of the ovules are fertilized and 

 produce seeds, it is found that the apple is rather one-sided. The seedless portion does not grow 

 as rapidly as the other, because the vessels conducting the food-materials are not so luxuriantly 

 developed. Thus, the position of the bundles in the wall of the core, their direct communication 

 with the seeds, and their sparing development when no seeds are formed, all point to an essential 

 relationship between the two. The branches from the main bundle supplying the seed spread 

 out over each carpel in the form of a delicate network (Fig. 94), and thus a regular and equable 

 distribution of food-material to the seeds is provided for. 



VASCULAR BUNDLES IN RELATION TO EACH OTHER. 



The primary vascular bundles in the apple, just as in other portions of the tree, do not 

 remain isolated and disconnected, but, by the anastomoses which take place, particularly towards 

 the periphery, there is continuity throughout. The entire system is comparable, in this respect, 

 to the anastomosing veins and arteries of the human body, only we must be on our guard against 

 speaking of "circulatory" tissues, or of the "circulation" of water or foods, as if there were a 

 central organ to and from which the nutritive fluids were directed. On the other hand, we must 

 remember that, even in the apple, there is a connected and not a scattered system of vascular 

 bundles (as Strasburger erroneously stated), which branch out from the stalk, and distribute 

 food-materials to every part, passing along each of the five chambers to supply nourishment to 

 the seed, and spreading outwardly among the cells of the flesh. 



To show this intimate relationship, it is not necessary to use the microscope, but simply to 

 macerate the apple, and remove the pulp, leaving behind the skeleton and the vessels, as in Figs. 

 83 and 88. Brooks (9), by means of frozen apples, was able to remove the soft flesh in water, and 

 show the large vascular strands giving off branches towards the periphery and over the carpels 

 But that wonderful network of vessels immediately beneath the skin, which also occurs in 

 stone-fruits, such as the plum, was unsuspected, and the means whereby the regular and equate 

 distribution of the food-material is carried out, in the region where the greatest and most rapid 

 growth occurs, was not then known. 



